High efficiency air cooling apparatus

ABSTRACT

An air cooling system consisting of several different known technologies brought together in combination to provide a complete cooling process. The invention may consist of several parallel and series stages in combination where each stage comprises an adiabatic stage which feeds a conventional heat exchanger. The conventional exchange of heat within the heat exchanger is assisted by an evaporation process where the water for the evaporation is supplied from water jets contained in the adiabatic stage and these jets are adjusted so that the water pressure is higher than is required for the adiabatic zone alone.

This relates to the treatment of air preferably but not exclusively within a data centre. The invention consists of apparatus designed to reduce the temperature of air within a room without the need, in normal circumstances, for the use of traditional refrigeration methods.

The invention consists of an embodiment of several different known technologies, which are brought together in a unique combination, in a manner which; until the present invention and it's disclosure in this description; has not been obvious to those skilled in the art.

There are many different methods of cooling air. The use of conventional electric compressor driven refrigeration means for air conditioning is by far the most obvious in today's technical environment, but this is by no means the oldest known method. Many technologies were known long before the use of electrical devices and most of these are related to evaporation of water or the addition of water to air.

These known technologies and their applications will now be further explained.

Conventional compressor driven refrigeration means in its simplest form is usually a closed circuit consisting of two interconnected coils of tube or pipe. Each coil is different, for air conditioning systems one is usually interwoven through a series of fins to form a heat exchanger and the other coil is usually spaced out so as to provide cooling for the liquid flowing through the coil. The coils are connected together through a valve at one end and an electrically driven compressor at the other end and the resulting closed circuit loop is filled with a substance called Freon which can either be a liquid or a gas.

Hot Freon gas is pulled from the heat exchanger coil compressed by the compressor which raises the boiling point of the gas and drives into the condenser coil where it condenses turning back into a liquid and cools. The cool liquid runs from the condenser through an expansion valve where it evaporates to become cold low pressure gas. Within the heat exchanger coil the cool gas absorbs heat from the air flowing through the heat exchanger and the gas becomes hot and because of the closed circuit continuous flow system it immediately returns to the compressor to begin the cycle again. In air conditioning systems the condenser is often another form of fin type heat exchanger and a separate electrically driven air flow is used to cool the condenser in which the Freon gas is turned back into a liquid.

These compressor based systems can provide extremely effective cooling but considerable energy is required to compress the gas. The energy needs of these systems is becoming an important consideration when planning an air conditioning system because in today's world the cost of energy can be prohibitive in some circumstances. Efficiency can be improved by use of different fluids and more efficient compressors and because of energy costs buyers are increasingly comparing the efficiency of systems which is often expressed as a “coefficient of performance” to simplify this comparison.

Another form of air cooling which is perhaps older than compressor driven systems is known as adiabatic cooling and these systems can be either direct or indirect.

An example of a direct adiabatic system is of course rainfall; it often feels cooler when it rains because the particles of moisture in the air absorb some of the heat. This principle can be applied to air cooling for a room and such an example can be found in US patent publication number 2010281896 where air is drawn through pads containing particles of water. The air gives off some of its heat to the water and the exhausted air is cooler. The disadvantage of this is that the exhausted air is also much higher in humidity because of the added water particles.

A further improvement on these direct systems was introduced in World patent number 2011/074005. In this example in order to reduce the consumption of mains water a heat exchanger was introduced in order to cool the water for re-use.

To avoid this increase in humidity indirect adiabatic systems were developed and an example of an indirect system for data centre cooling can be found in GB patent number 2464284. In this example a first air flow of external air is drawn in through an adiabatic cooler. This adiabatic unit is either a pad system as in the previous example, or a water spray system where water droplets are added directly to the air. The first air flow of cooled air is then fed to a heat exchanger before being exhausted to the outside of the building. A second air flow which does not mix with the first is drawn from the room to be cooled and fed through the heat exchanger where the cooler moist air from the first air flow absorbs the heat from the second air flow. The second air flow of now cooler dry air is fed back into the data centre room to be cooled.

In order to create a method of cooling air which was better that these adiabatic systems direct injection evaporative systems were developed. An example of such a system is given in European Patent number 1946027. In this example a heat exchanger is used as in the previous example, however, here the water is sprayed directly on to the surfaces of the heat exchanger. Water is inserted at the top against the first air flow which is in an upwards direction and the water drops down into a bottom sump. This first air flow is directed upwards across the wetted surfaces of the heat exchanger and an evaporation process takes place which removes heat from the surface of the heat exchanger and that heat is exhausted into the atmosphere. A second air flow is entirely separate from the first. It is drawn from the room to be cooled and fed to the heat exchanger where heat from this first air flow is deposited on to the plate of the heat exchanger so that the second air flow of now cooler air can be fed back to the room to be cooled having never mixed with the first air flow.

Further improvement can also be seen in the above example where conventional refrigeration means are also included so that on the rare occasion where the evaporative means is not sufficient then conventional compressor driven means can be used to supplement to evaporative means.

The present invention is a unique combination of all technologies previously described with added features to improve cooling and overall efficiency.

In this specification a “first” air flow consists of air drawn from the atmosphere outside of the building in which the area to be cooled is contained and is also known as “external air” or “air flow X”. A “second” air flow consists of air drawn from inside of a building which is cooled and then fed back to the same building and is also known as “Internal air” or air flow “Y”. The first and second air flows do not meet and are not mixed in any way but they both pass through different channels in the same heat exchanger. Adiabatic cooling refers to the introduction of atomised water spray to air and evaporative cooling refers to the passage of air over wet surfaces where the said air absorbs water which evaporates from the said wet surfaces. The word “section” refers to a portion of the heat exchanges consisting of various passages through which air flows. The word “stage” refers to one cooling unit consisting of a combination of adiabatic cooling and a heat exchanger. The word “channel” refers to an air flow through the system which may be external air also referred to as X air or internal air also referred to as Y air.

According to the invention, an air cooling system is contained within a suitable housing and has first X and second Y air flows which are not mixed. The first air flow X is external air and upon entering the housing the air passes through an adiabatic zone containing a water atomising spray where the external air X is mixed with water droplets discharged from atomising nozzles causing a drop in temperature as the water droplets absorb heat from the air.

In a second aspect of the invention the external air X moves from the adiabatic zone into a heat exchanger. This heat exchanger is plastic composite plate type where heat is transferred between two different and separate air flows. The pressure of the said water atomising spray is set much higher than is necessary to operate the adiabatic zone so that water spray travels through the adiabatic zone into the said heat exchanger. The heat exchanger is divided into two sections a first section through which the first air flow X travels and a separate and unconnected section through which the second air flow Y travels. The water spray enters the first section of the heat exchanger, which has its internal surface area treated so that it is hydrophilic and therefore the water spreads evenly upon the surface of the heat exchanger. Warm X air entering the heat exchanger from the adiabatic zone causes the surface water to evaporate, transferring heat from the surface of the heat exchanger to the moving first air flow X causing an increase in the temperature of the first air flow X and a drop in the temperature of the surface of the heat exchanger.

A second air flow Y passes through each heat exchanger through a second air flow section carrying internal air Y. This air, Y, is taken from the room to be cooled and fed through the heat exchanger where heat is transferred to the cooled internal surfaces of the heat exchanger thus cooling the air and warming the internal surfaces and the X air stream in the heat exchanger.

The heat exchanger is therefore fulfilling two separate purposes firstly it is acting as a straightforward heat exchanger drawing heat away from the inside air Y and transferring into the adiabatically cooled air X and secondly it is acting as an evaporative cooler drawing even more heat from the internal air Y into the evaporatively cooled internal surface of the heat exchanger and transferring it via evaporated water to the adiabatically cooled first air flow X as it passes through the heat exchanger both processes are occurring at the same time in the same first air flow section of the heat exchanger.

Warmer first air flow X flowing out of the heat exchanger may then enter further adiabatic cooled zone/heat exchanger stage or stages and the process in this further stage or stages is exactly the same as has been previously described for the first stage. The cooling system therefore may have more than one stage in series, though the water pressure and flow characteristics in the second and any further stage adiabatic zones may be different from the first.

Where there is more than one stage, the secondary air flow Y in the unit described above may be divided into parallel air flow channels so that a separate Y air flow channel is available for each of the series stages. Thus a flow equal to Y1, Y2 and so on is formed to feed each of the additional adiabatic/heat exchanger series stages.

A further aspect of the invention adds another cooling means to the second air flow of internal air Y. Water which is supplied under pressure to the adiabatic zones, passes first through a separate heat exchanger in which the cool water is used to further reduce the temperature of the secondary internal air Y which passes through this separate heat exchanger before it is passed back to the room to be cooled. This heat exchanger is constructed differently to the plastic composite plate type in that it is as water to air type using well know technology similar to that used for a car radiator or oil cooler. A different heat exchanger is used for each of the internal air flows or Y channels.

In another aspect of the invention the system of one stage or more than one series stages described above, is supplemented by further parallel stages which repeat the one or more stage series construction previously described where each stage contains an adiabatic zone and a heat exchanger. In a preferred embodiment there are three parallel stages splitting the first air flow X into three separate parallel first air flow channels, X1, X2, and X3. This system therefore contains 6 adiabatic sections and six plastic composite plate heat exchangers. The second internal air flow Y in this arrangement is still two parallel air flow channels Y1 and Y2.

A further aspect of the invention deals with by-pass air flow. Internal air Y enters the air cooling system and if necessary is divided into more than one Y channel. A further bypass Y channel is also available but a modulating damper in the path of air flow is usually closed preventing air flow in the bypass channel. If the temperature in the Y air flow from the final heat exchanger is sufficiently low the modulating damper is opened and the air flowing through the plastic composite plate heat exchangers is bypassed by air flow which does not pass through the plastic composite plate heat exchangers. Air flows through the heat exchangers are not closed off but the air flow reduces because path the bypass channel has less resistance than paths which have to pass through the plastic composite plate heat exchangers and the water to air heat exchangers.

A further aspect of the invention relates to additional conventional air conditioning apparatus to provide supplementary cooling. In the event that the outside air is very warm and the system cannot cool the air to the required temperature standby conventional compressor driven closed circuit air conditioning apparatus is built into the system. In series with the internal air flow Y there is an additional fluid/gas to air heat exchanger for each Y channel coupled to a compressor and linked to a condenser coil which is located in the exhaust external air flow of the X channels.

This compressor driven close circuit system is not normally in operation but is called into operation by the system's electronic control when sufficient cooling cannot be obtained from the adiabatic and evaporative stages.

Water supplied to the adiabatic system is drained down by gravity after passing through the heat exchangers into a sump at the bottom of the system housing where it is drained. However in situations where the constant supply of fresh cool water is not an option, water may be re-circulated after cooling in effect making a closed circuit water system with provision for volume make up.

Finally the system will incorporate water filters and water pumps to treat and drive the water flow also electrically driven fans to drive both air flows X and Y. In some embodiments also there will be suitable air filters.

In overall command is an electronic control system which monitors external air intakes, external air exhaust, all air flow between sections and internal air flows. Monitoring may be for temperature and/or humidity and air differential pressures and the said control system can regulate all fan speeds, water pressure, and modulating damper control. Additionally it can also bring into operation the supplementary compressor driven air cooling when required.

The invention will now be described by way of example with reference to the accompanying drawings in which—

FIG. 1. Is a plan view of the invention showing all aspects of the system.

FIG. 2. Is a cut away view showing the construction of a plastic composite plate heat exchanger as used in this system.

Referring first to FIG. 2, this is a typical cut away view of a plastic composite plate heat exchanger. There are two air flows X and Y and they do not mix. The X and Y channels are separated by a thin membrane 39 of suitable material, usually plastic. Heat or cold is transferred from one air flow to the other though the membranes 39 separating the two air flows. In this illustration the shaded portions 40 are edge filled to prevent leakage of air from one channel to the other. The surfaces 41 of the heat exchanger which carry external air X are treated so as to be hydrophilic so that water can be more evenly distributed over the surface area of the channel separation membrane.

Referring now to FIG. 1, this example show a two stage series arrangement for X air flow coupled with a three stage parallel arrangement for Y channels. Air from the atmosphere outside of the building to be cooled enters the air cooling system and is divided in three channels X1, X2 and X3 the air is pulled into the system by fans 33, 34 and 35. In channel X1 the air first passes through the water atomising spray 27 and enters adiabatic zone 21 where it is cooled. The cooler air together with water from the atomising nozzles 27 then enters the plastic composite plate heat exchanger 6 where it collects heat from the internal surfaces of the heat exchanger. This occurs by the natural transfer function of the heat exchanger and also by evaporation so there are two processes here occurring simultaneously.

The warmer air X1 which leaves heat exchanger 6 passes through atomising spray nozzles 30 and enters adiabatic zone 24 where it is cooled before entering heat exchanger 7 where once again it picks up heat from the separation membrane and warms up. The warmer air now humid, passes through fan 33 and then through condenser 21 and is exhausted to the atmosphere. There are therefore two stages in the channel.

This two stage series flow arrangement where adiabatic zone 21 is followed by heat exchanger 6 then by adiabatic zone 24 followed by heat exchanger 7 followed by fan 33 is repeated. There are three parallel channels X1, X2 and X3 which are each identical to the X1 channel previously described. X2 channel consists of the two stage series arrangement comprising adiabatic zone 22 followed by heat exchanger 8 followed by adiabatic zone 25 followed by heat exchanger 9 followed by fan 34. X3 channel consists of the two stage series arrangement comprising adiabatic zone 23 followed by heat exchanger 10 followed by adiabatic zone 26 followed by heat exchanger 11 followed by fan 35 and each of the three channels then exit through condenser 21.

Air from the room to be cooled is referred to as Y or internal air is fed into the system at the top of FIG. 1 again there are three parallel channels but in this case only two Y1 and Y2 are identical. Y1 and Y2 air channels feed through the series heat exchangers and heat is transferred to the X air flow though the membrane which separates X and Y air flows within the heat exchangers. Y air passes through each of the three parallel X channels and is cooled a little more each time it passes through a heat exchanger. Next the Y1 channel air passes through the water cooling heat exchanger Z13 and the Y2 air passes through the water cooling heat exchanger Z12 before entering the optional refrigeration heat exchangers 19 and 20. The Y air then passes through fans 36 and 37 and is exhausted to the room to be cooled at Y6.

The bypass channel Y3 is brought into use by opening modulating damper 38 and Y3 air is combined with Y1 and Y2 air to form Y4 and Y5 respectively and exhausted at Y6.

The cold water supply enters the system at Z16 is pumped at Z14 and filtered for minerals and treated at Z15 before being fed to the water to air heat exchangers Z13 and Z12 previously described. Water is then fed to the atomising spray nozzles in the adiabatic zones.

Used water drains down from the adiabatic zones and the heat exchangers into a sump Z18 where it is drained away at Z17. In some areas water conservation requires a re-cycling system and where appropriate such a system is employed between Z17 and Z16. This would use conventional technology and may incorporate a storage tank and/or a further heat exchanger.

Conventional refrigeration is used in exceptional circumstances and a condenser is placed in the X exhaust air flow whilst a gas/liquid heat exchanger or exchangers are placed in the Y air flow at 19 and 20.

It will be appreciated that many different variations on this system are possible both in terms of the number and positioning of heat exchangers and adiabatic zones. However the combination of adiabatic, evaporative and direct transfer is unique together with the addition of the other cooling means in combination as described.

In a further embodiment, not shown in the drawings, air flow X which is normally discharged to the atmosphere is re-circulated to the external air intake via a series of dampers. This is for operation in exceptionally low ambient temperatures down to −40 deg C. where there is a need to maintain an air onto the external heat exchanger above −8deg C. to avoid condensation on the internal surfaces of the heat exchanger. 

1. Air cooling apparatus which includes a first air flow which cools a second internal air flow, in which the first air flow and the second internal air flow both pass through different channels in the same plate type heat exchanger, inside of which heat exchanger the said first and second air flows do not mix, characterised by the first air flow passing initially through an adiabatic cooling zone before entering the said plate type heat exchanger within which the second air flow is cooled by transfer of heat to the first air flow which has been cooled by the adiabatic cooling zone.
 2. Air cooling apparatus according to claim 1 where within the said plate type heat exchanger additional cooling is achieved by the provision of an evaporative cooling process where the first air flow collects heat from the second air flow by a process of evaporation of water on the surface of the heat exchanger plates over which the first air flow passes.
 3. Air cooling apparatus according to claim 2 where the water for the said evaporative process within the plate type heat exchanger is supplied from outside of the plate type heat exchanger.
 4. Air cooling apparatus according to claim 3 where jets which supply water to operate the adiabatic cooling zone are adapted to also supply water to the plate type heat exchanger for use by the evaporative cooling process within the plate type heat exchanger.
 5. Air cooling apparatus according to claim 2 where the adiabatic cooling zone and the plate type heat exchanger containing an evaporative cooling process as described are together known as a stage and where the stage is repeated one or more times so that there is a further adiabatic cooling zone and a further plate type heat exchanger containing a further evaporative process such that the first air flow travels first through stage 1 and then through stage 2 and then through any further stages in series.
 6. Air cooling apparatus according to claim 5 where the second air flow may be divided into separate air flows to feed the said stages 1 and 2 and any further stages in parallel.
 7. Air cooling apparatus according to claim 6 in which the water supplied to the adiabatic zones passes first through a separate heat exchanger or exchangers in which the cool water is used to further reduce the temperature of the second internal air flow.
 8. Air cooling apparatus according to claim 6 where each stage or series of stages may be repeated so that the first air flow may be divided into more than one channel to pass through parallel sets of series stages.
 9. Air cooling apparatus according to claim 8 which includes bypass channels for the air flow to be directed to circulate without passing through any cooling stage.
 10. Air cooling apparatus according to claim 9 which includes a conventional refrigeration apparatus to supplement to said cooling stages. 